Spark gap device



Feb. 9, 1960 q, LP-PLE y 2,924,734

SPARK GAP DEVICE Filed May 28, 1956 WITNESSES Johannes-I 'p Yle v/W BY J. K

ATTOR EY INVENTOR United .,Staf1affif 0."

2,924,134 l SPARK 'GAP' DEVICEl Johannes Lpple, ,Berlin-Siemenssmdt, Germany, assigner to Siemens-Schuckertwerke Aktiengesellschaft, Erlangen, Germany, a corporation of Germany Application May 28, 1956, Serial No. 587,733 claims priority, application Gemnmysune 9, 1955 3 Claims.` Cl. 3131-401) i The'present invention relates to spark gap devices and, more particularly, to an improved spark. gap having a low andconsistent-impulse ratio and which is .especially suitable for usewith valve4 type lightning varresters .or

other protectivedischarge devices. `Lightning arrcsters for'the protection vof transmission or .distribution lines, or `other, electrical devices, yusually consist of. a spark gap connected in series-with a non- `linear resistance or ,valve 4element which hasthc property of sharply decreasingits. resistance when a predetermined:

voltage is applied to it so that it permits the passage to ground of relatively largecurrents with low discharge f `than the 60 cycle or normal frequency spark-over voltage.

The ratio of the spark-over voltage under a standard test surge to the static or normalirequen'cy sparkover voltage is called the impulse ratio of thegap, and it is desirable to make this ratio as near-v to -unity `as possible. T-he high spark-over voltage under surge. conditions is due to a tirnerlag after the surge rises above the lstatic, spark-over before the gap actually sparks' over. It will be obvious, therefore, that in order to obtain low impulse ratios it is necessary to reduce the delay ingap sparkover. "It is apparent that low'impulse ratiosjare desirable since sparkover at the lowest possible voltagey is desirable in a device such as a lightning arrester to improve its protective characteristics. In order to reduce this delay in gap sparkover, various means have been proposed to preionize the air in the gap and thus tio cause production of large numbers of free electrons which in turn cause rapid breakdown of the gap with a minimum time lag. Someof these means include irradiation of thespark gap with ultraviolet rays or by means of radioactive substances. These means are costly and hazardous to persons engaged in manufacturing the device. The present invention*` provides means for preionizing the air gap which facilitates manufacture and eliminates hazard to persons engaged in manufacturing the device.

It is an object of the present invention to provide a simplied construction of a spark gap device in which high local voltage stresses will be produced when a rapidly rising voltage is applied across the gap in order to obtain a low breakdown voltage.

More specitically, the object is to provide the inner and outer walls of an extinguishing chamber of the spark gap device with at least partially overlapping metal coatings in order to produce a glow discharge near the spark gap at voltages below the static spark-over voltage of the spark gap, whereby the glow discharge ionizes the spark gap.

AFurther objects of my invention relate to constructional details of the spark gapdevice which reduce th` facilitate manufacture of a spark gap device.A My invention contemplates the use ofmetal lcoatings on the inner and outer walls of a chamber-enclosing the 'spark gap device, which coatings are each connected to one of the electrodes. The metal coatings' overlap at their ends adjacent the spark gap whereby a glow dis` ,charge will occur at this point and will ionize the spark gap between the electrodes, thus reducing the`delay in sparkover. lIt is necessary or atleast desirable that the glow discharge occur at a somewhat lower voltage than the static sparkover voltage, for satisfactory operation. Thus, the wall of the enclosing chamber may be reduced in thickness in the region of the'spark gap where the inner and outer coatings overlap. By appropriate `selection of the distance between the coatings and by selection of a material of suitable dielectric constant for the walls, v

a glowdischarge at a voltage lower than the static sparkover voltage can be obtained. For satisfactory operation, it is also necessary that the distance between the gap elec- -trodes be .smaller` than the shortest distance between the inner metal coating and the opposite electrode. will prevent sparkover between the coating and .the electrode. Such sparkover would burn out the metal coating and shorten the useful life of the gap device.

The invention will be more fully understood from the following detaileddescription, taken in connection with the accompanying drawing, in which:

Figure 1 is a sectional view along line I-I of Fig. 2,

and

Fig. 2.is a plan view of the device, partly in section,

with the upper wall of theextinguishing chamber removed;

The gap device shown in the drawing-for the purpose of illustration includes two metal electrodes 1 and 2 .spaced apart Ito `form 'a vspark gap between them. As shown in Fig. V2, each electrode is preferably provided with two hom-shaped projections 3 and 4 along which the terminals of the arcrnay move. A permanent magnet 14 as'. shown or any other suitable arc blowingv arrangement may be provided to inuence movement of the Aarc along .the electrodes and to facilitate the extinction of the arc. The electrodes 1 and 2 are disposed in longitudinal alignment between a -pair of walls 6 and 7.

The wall members are sheets of dielectric material. .An extinguishing chamber 5 is formed by the pair of walls 6 and 7 of dielectric material.

Metal coatings 9 and 8 are provided on the inside and outside walls respectively of plate 7. Metal coating 8 is connected with electrode 1 and metal coating 9 is connected with electrode 2. One end 10 of the inner metal coating 9 is disposed near the spark gap in overlapping relationship to the adjacent end of outer metal coating 8. At their center portion 11 near the gap between electrodes 1 and 2, plates 6 and 7 are reduced in thickness to provide proper spacing of metal coatings 8 and 9 and electrode 1. Since the voltage is concentrated between the inner and outer metal coatings 9 and 8, respectively a smaller distance between the metal coatings will produce a lhigher ield strength at a lower voltage. Therefore, by reducing the thickness of the plates 6 and 7 in the region where the coatings overlap, suticient eld strength to obtain a glow discharge is obtained at a voltage lower than the static spark-over voltage. The distance between electrodes 1 and 2 is made smaller than the shortest distance between the electrode 1 and the metal coating 9 in order to prevent sparkover between metal coating 9 and electrode 1. An electric eld between the electrodes 1 and 2, and between the coatings 8 and 9 is built up when a voltage surge occurs. Due to the high eld strength at the point 10, a glow discharge will occur at this point which will ionize the air in the spark gap between elec;

Patented Febf9, 1960..`

This

trodes 1 and 2, thus reducing the delay in sparkoverbetween electrodes 1 and 2. Since the distance between electrode 1 and inner coating 9 is greater than the distance between electrodes 1 and 2, the arc will occur only between electrodes lfand 2 and' not between inner leo'ating 9 and electrode 1.

Electrode 2 is adapted to be connectedv to a transmissionV or distribution line or other electrical device to be protectedr and electrode 1 is connected in series to a 'suitable valve-like resistance element .12'which is connected to ground as indicated at 13. In accordance with my invention, corresponding coatings 'may also be provided on wall 6, if desired. u

As shown in the present embodiment of the invention, the coating 9 is made narrower than the electrodes, as can be seen in Fig. 2, 'so' that the coating will not be contacted by the moving terminals of the arc, as it is'shielded from the arc by t-l 1e1electrode.`

A suitable number ofthe above-described spark gaps can be connected in the usual manner in series,` if desir'ed.

Itis to `be understood that although a specific embodiment ofthe invention has been illustrat'edfand described, it is not limited tothe exactiarrangem'ent shown, but that in "itslbroadest aspe'ct'it'includes' all'equivalent embodiments and modifications.

I claiin'as my'in'vention: -Y

1. Asparkgap device comprising, a pair of longitudinallyv aligned -,electrodes forming 'a spark gap therebetween, a sheet'ofdielectric material bridging'said gap, a metallic coating on one side ofsaid dielectric sheet connected to one of said electrodes, a metallic coating on the other side of said`dielec`tric sheet connectedt the other electrode, said metallic coatings overlapping each other adjacent said gap to -elect a glow dischargel between the metal coatings when predeterminedivoltage occurs be tween the lelectrodes whereby saidfgap is lionized thus reducing the delay in gap sparkover.

' 2. A spark gap device comprising a dhamberhaving a pair of walls of dielectric material, an inner rnetal coating on .the inner side of`orie of said walls, an outer metal coating on the outer side of said one wall; a pair of electrodes between said wallsextending in-to said chamber forming a-spark gap between theelectrodes; `said inner metalcoating being connected to one electrode of said pair of electrodes; 'said outermetal coating being connected to lotherv electrode of said pair ofi electrodes, the free end lof said inner and outer metal coatingsv adjacent ythe sparkgap beinl'gidisposediindan overlapping relation* ship; the shortest distance between. said inner metal coating and said other electrode being greater than the distance between theksaid one electrode and said other electrode to prevent ashover between the inner met-al coating and said other,A electrode; and said walls being reduced in thickness adjacent said spark gap, the distance between said innen prrrtferI Irnetal coatings adjacent the gap b smaller lthan the distance between theelectroas", W h'frg" will occur'between saidcoatin ragegthjaii'the 'sparkover voltage betw n said es*v thereby' preioniiing said chamber.

3- le a ,light-eier; arreter, a Spark gap defies .comprising' a y"rs't' "lectril and ia' "ecoid' electrdd; said electrodes spaced apart Inform a spark gap `between them, a sheet of dielectric material disposed adjacent to and bridging said gap, a conductivecoating on each side 'of sai/d sheet, vsaid sheet "being" 'of such thickness' as to obtain a'glow dischafg'ebetwee'n the cnduct'ivecoatin'gs at 'a' "predetertrlinedvo1tag`e, s'aid `predetermined voltage being "lower 'than' the 'ga'p"spakoveij'vbltageg4 one of said conductive coatings beingelec'tiicllyconnected to `said rsteleetroiejmeetheofsaid conductive coatings being y osaid secondelectrodfsaid'one cen'dtnztiv-eV coating svpa'cjedwfri said second electrode'a drstan'ce greater than'fthidsftnee"between said rst `and Seeond'electr'vode 'and said other' ca'tingf'spacedfrom said irstelectrotle'a'distance"greater than the distance between ,Refeeseie ie the, file y"fthe new UNITED STATES PATENTS l Re. d20,455 `Brach Aug. 10, 1937 1,604,986 Nov. 2, 1926 v1,984,428 \"De c."18,` 1934 2,068,741 Y IIan. y26, 1937 2,164,720 j l Iu1y`4, 1939 2,228,327 Spanner` Jana 14, 1941 2,249,672. Spanner July 15, 1941 12,462,336 Feb. 22, 1949 2,503,911 Kalb Apr.A 11, 1950 A2,591,370 Nelson "Apr. 1, 1952 2,620,452 Petersen Dec. 2, 1952 :644,113 Etz-kern Juneso, 1953 2,663,817 De'Val'f 'Dec. 22, 1953 2,774,013: Dec.' 11,` 195,6 

1. A SPARK GAP DEVICE COMPRISING, A PAIR OF LONGITUDINALLY ALIGNED ELECTRODES FORMING A SPARK GAP THEREBETWEEN, A SHEET OF DIELECTRIC MATERIAL BRIDGING SAID GAP, A METALLIC COATING ON ONE SIDE OF SAID DIELECTRIS SHEET CONNECTED TO ONE OF SAID ELECTRODES, A METALLIC COATING ON THE OTHER SIDE OF SAID DIELECTRIC SHEET CONNECTED TO THE OTHER ELECTRODE, SAID METALLIC COATINGS OVERLAPPING EACH OTHER 